This is the supported limit for the model and Image you are running (LAN Lite)
https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-2960-series-switches/product_data_sheet0900aecd806b0bd8.html
You also cannot upgrade from LAN Lite to LAN Base. It is fixed. I don't believe there is a way to increase the supported vlans without buying a new physical unit running LAN Base or higher.
Are all the vlans currently configured in use by you?
Thanks